A variety of techniques are known for forming multiple strips of a composition onto a substrate. In those processes, a composition is applied to a web in the form a plurality of strips, each of which is separated from an adjacent strip by a region which is uncovered. One example of an extrusion type apparatus used in this type of process is described in U.S. Pat. No. 4,106,437, incorporated by reference herein. Extrusion type dies are disadvantaged in that as the composition is extruded onto the substrate, the composition can “neck down” or decrease in width and thickness between the exit of the die and the substrate. In certain applications, this method cannot generate sufficiently precise strip widths and thicknesses.
An alternate process for applying strips to substrate is contact coating type dies. In contact coating, the die is disposed close to the substrate so that “necking down” of the composition is eliminated. Thickness of the composition is adjusted by pulling the composition through a clearance between the substrate and an obstruction. When the end process involves dispensing relatively viscous material (e.g., greater than 1000 centipoise) the coating die can be subjected to high pressures which act to deform the structure of the die. A common required characteristic of the strips is a uniform cross-sectional profile. Deflection of the die can result in a non-uniform cross-sectional profile of the flowable material being coated onto the substrate. An additional requirement in certain applications is to maintain the edges of the strip of flowable material to a high level of precision (e.g., perpendicular to the substrate). Additionally, in some contact dies, as the substrate moves relative to the die, it is common for the substrate to wear on a portion of the die so that this portion would eventually require replacement. The rubbing of the substrate on the die can also cause a “necking down” of the web, potentially causing variation in strip width. This “necking down” can also affect the variety of substrates which can be used with the die.
Achieving a precise profile of the strip of flowable material along with precise edge definition as well as decreasing the amount of wear on the die are desirable improvements in strip coating technology. In particular, the uncoated portion of the substrate typically is the portion of the substrate which wears on the die. Thus, as the uncoated portion of the substrate increased, the wear of the substrate on the die increased, having the effect of limiting the percentage of uncoated substrate which can be manufactured due to the high wear of the die.